Owen Howkins has Schwartz-Jampel syndrome, a rare condition that causes the 8-year-old boy’s muscles to be permanently tense, leaving him in such pain that he is afraid to even go outside and terrified of interacting with strangers.

But that changed when he met Haatchi, a three-legged Anatolian Shepherd dog adopted by his parents who has now become his best friend. The special bond between Owen and Haatchi was featured in a now-viral YouTube video, one that’s sure to induce some tears from viewers.

Like Owen, Haatchi has a sad story. The dog was tied to a railroad line in London and 2012 and struck by a train. As a result he lost his back leg and tail, but managed to survive.

Owen’s father Will and mother Kim had split, and Will remarried a New Zealander named Colleen Drummond who happened to be a dog trainer. When Colleen came across the enormous dog online she fell in love instantly, knowing that somehow the dog was needed in their lives.

“Haatchi responded equally strongly to the child he now saw it as his duty to protect,” she said.

Owen Howkins and Haatchi look like an odd pair. Owen is small and has difficulty maintaining his balance because his muscles are always in a state of tension, but he looks at ease when he lays into the dog nearly three times his size.

Owen’s parents say that Haatchi has opened him up in other ways too. Once terrified of strangers, Owen now loves talking to people about Haatchi and sharing the dog’s amazing life story.

The story of Owen Howkins and Haatchi is also being told through a new book, Haatchi and Little B, which was released last week. Hundreds of people showed up to a book signing this weekend to meet the boy and his dog.